feat(processor): allow composes anywhere in a rule

[tivac]

Description

BREAKING CHANGE: previously modular-css would require that composes be the first declaration in a rule. This restriction has been removed due to better solutions for enforcing that behavior existing now (stylelint-order).

Motivation and Context

Fixes #645

How Has This Been Tested?

Tests! Also gonna poke at it in the REPL once the PR goes up.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov]

Codecov Report

Merging #646 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #646      +/-   ##
==========================================
- Coverage   99.13%   99.12%   -0.01%     
==========================================
  Files          46       46              
  Lines        1150     1143       -7     
  Branches      174      173       -1     
==========================================
- Hits         1140     1133       -7     
  Misses         10       10

Impacted Files	Coverage Δ
packages/processor/plugins/composition.js	100% <ø> (ø)	⬆️

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